Development On Optical Current Transformer Testing Platform Based On DSP Chip

Optical Current Transformer (OCT), based on the Faraday Magneto-Optical Effect, is excogitated as a novel current measurement device which takes the optical fiber as a medium. It has many advantages, such as fast response, easy interfacing with digital devices and non-core. So in power system application, the OCT is paid great attention and given good development space. In the future, the traditional electromagnetic current transformer will be replaced by the OCT.In this paper, based on the OCT's measurement principle and structure design, three kinds of signal measurement schemes which are single light path, dual light path and improved dual light path have been made comparison. The data processing algorithm is analysed. The system mathematical models and block diagram are established. The expression of output light is deduced. That the linear birefringence and instability of laser source hindered the OCT's practicality is realized.In this paper, the optical current transformer testing platform which based on the analysis of the OCT's signal measurement scheme and digital signal processor (DSP) is designed. The two parts of testing platform are measurement system and simulated light intensity generator. In measurement system hardware, dual-optical signal measurement processing scheme is adopted. The programmable differential amplifier is taken to accomplish subtraction operation. Traditional analog division operation is realized by software for eliminating interference signals introduced by analog divider. These technologies and improved analog filtering are adopted to effectively improve the performance of hardware system. The hardware circuit is simulated by PSpice. The results show that the accuracy in measuring current signals is improved and the frequency response range is broadened. In measurement system software, the high-order FIR digital filter technology designed by using window functions method is used for filtering sample values. The designed FIR digital filter is simulated by Matlab. The results show that, FIR digital filter is effectively used to suppress noise, filter clutter signals, improve measurement accuracy and restore the original signal.In laboratory environment, based on practical principles, a simulated light intensity generator is designed by DSP and D/A module to produce a signal whose waveform is variable and frequency is adjustable. A controllable light signal produced by generator is used to test the measurement system. The results show that the current signals could be well restored by the DSP-based OCT's measurement system which is practical and has good dynamic performance.